The U.S. Office of Education has agreed to release $12 million of federal-impact aid funds for Washington area schools that had been threatened with impoundment, Rep. Newton I. Steers Jr. (R-Md.) disclosed yesterday.

Despite the release of funds for the current fiscal year affected by the announcement, the fate of such aid in future years remains in doubt. Funds for the program, totaling $400 million nationally and $28 million for this region, were omitted from budget requests made to Congress by former President Ford and by President Carter.

There were two new developments, one an advance and the other a setback for the program, which compensates school systems for part of the cost of educating children of parents who work on untaxed federal property.

Rep. Herbert E. Harris (D-Va.) submitted to a House Appropriations subcommittee a letter signed by 100 members of the House from 36 states urging that full funding be granted. The letter said a loss of the funds "will force local governments to boost homeowner property taxes."

Rep. Robert N. Giaimo (D-Conn.), chairman of the House Budget Committee, told a news conference that he supports the President's proposal to kill the impact program, although he would not oppose a phasing -out period. Giaimo said the program rewards such wealthy counties as those in the Washington suburbs.

Steers said he was told of the restoration of the current fiscal year's funding by William F. Pierce, acting education commissioner for the Department of Health, Education and Welfare.

Steers said the $12 million for this area is part of an estimated $15 million nationally. It affects only a category of payment that is common here but unusual elsewhere: compensation for students who go to school in one state (Maryland, for example) while their parents work elsewhere (in the District of Columbia or Virginia, in this example).

Steers said he was informed by Montgomery County school officials that the government was considering the imoundment of funds in this category. Payments for other classes of students were not affected.

Unofficially, approximate sums involved would be: Montgomery County, $2 million; Prince George's, $3.3 million; Fairfax County, $1.2 million; Arlington County, $600,000; Fairfax City, $50,000; Alexandria, $185,000 and Falls Church $13,000, with the balance going to outlying Virginia and Maryland countries.